rViz does not reflect my initial pose

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I am using a blank map and setting the initialpose by publishing to the initialpose topic. I expected that rViz would subscribe to this and that the initial pose in rViz would reflect it. But publishing different initial pose's does not change the initial location of my robot in rViz. Why is that?

I guess I don't understand how rViz should respond to initialpose messages. I run the rbx1 fake_nav_test and either manually in rViz or use rqt_publisher to send an initialpose message. I expect the robot to jump to the initial pose on the rViz screen, but nothing happens. This is all in the map reference frame.

I am using an example from ROS By Example Volume 1. The files are here: https://github.com/pirobot/rbx1 and I am using rbx1/rbx1_nav/launch/fake_nav_test.launch. I run roslaunch rbx1_nav fake_nav_test.launch.